The present invention relates to devices and methods for thermally breaking down waste products such as refuse, producing recyclable commodities, recovering waste heat and converting the same to energy.
Solid waste, such as refuse, medical waste, toxic wastes, oilfield sludge, sewage sludge, chemical wastes, discarded tires, contaminated soils and the like continue to present global problems concerning disposal. For non-toxic refuse and municipal wastes, the most typical approach is to bury the same in landfills. As landfills become full, the problem of where and how to dispose of solid wastes increases. While it has been known to compact such solid refuse waste, compaction will only increase the life of a landfill and simply put off the problem until the landfill is full.
Toxic and chemical wastes suffer from the same problem. Modernly these wastes, which may be sludges, contaminated soil from an environmental clean up such as Brownfields sites, or a broad spectrum of other wastes are sent to specially designed, lined, landfills. These wastes, are typically stabilized with products such as by being mixed with dry Portland cement and then moved to the lined landfill. Again, sending such wastes to landfills does not treat the waste, reduce waste weight and volume and/or eliminate the on-going liabilities to the waste generator.
Eventually, as toxic landfills become full, more disposal sites will have to be procured at enormous financial costs to public, private and governmental groups.
Another problem particularly associated with toxic landfills is that they are usually sited in remote locations. Both environmental groups and the public at large have adopted a policy of rejecting placement of landfills in their geographic areas. Thus, wastes must be transported long distances to landfills, thereby significantly increasing the chances for accidents or toxic spill incidents during transportation and increasing the costs of disposal.
Past practices have been known to bum or incinerate refuse and toxic waste. Due to increased governmental and regulatory standards, the potential health impacts of carcinogenic air emissions, such as dioxins and furans to the public and the risks of spreading toxic plumes, the burning of wastes, for the most part has been abandoned.
It is known to recycle wastes such as paper, plastic, aluminum, glass, metal and the like: however, there remains a large volume of refuse waste which cannot be recycled.
One product which has contributed to landfills is used tires.
In Hansen et al, U.S. Pat. No. 4,759,300 titled Method and Apparatus for the Pyrolysis of Waste Productsxe2x80x9d and issued Jul. 26, 1986, the disclosure of which is hereby incorporated by reference, a method and apparatus for the pyrolysis of waste products is disclosed. According to this patent, the sludge is pumped to a pre-processing unit which drives off moisture for the sludge. The dried material is fed to a double-pass retort where the material is moved through a first pipe (defining a first retort) with a screw. The pipe is externally heated with a natural gas burner to pyrolize the waste material. The material is then passed through a second, externally heated, screw retort to an outlet. The gases from pyrolysis in the first and second retorts are collected to be used to fire the burner. The combustion gases are vented to atmosphere.
In Hansen et al U.S. Pat. No. 5,653,183 titled xe2x80x9cPyrolytic Waste Treatment Systemxe2x80x9d issued Aug. 5, 1997, the disclosure of which is incorporated by reference, discloses a system where waste material is metered by two valves into a single, specially configured retort having a screw. The retort is heated by external burners and some of the gases produced by the pyrolysis of the waste is fed back into the front end of the retort. The retort off games are sent to a thermal oxidizer where they are combusted in a natural gas burner. The gases from the thermal oxidizer may be sent to a waste heat boiler.
A drawback to prior devices and systems is that the heated retort is relatively long to provide for pyrolysis along its length. That is, according to the prior art external heat is applied externally to the retort for complete pyrolysis along the heated length. Since conventional thinking required external heating along the substantial length of the retort the same requires (i) a long retort and (ii) a long combustion chamber to accommodate the long retort. This requirement of externally heating the retort along its length and the corresponding long combustion chamber has contributed to the expense of pyrolysis units.
Still further the requirement for pyrolysis to be accomplished along the length of the retort and because the nature of the material being moved through the retort has contributed to the axial length and size of the retort making units unsuitable for transportation or for trailer mounting. It would be advantageous to provide a unit where the pyrolysis could accomplished with a relatively short retort apparatus and where the combustion chamber is of a minimum size.
It would also be advantageous to provide a device and system which provides for substantially continuous feed rather than slug feed as hereinafter used in the systems described above.
It would also be advantageous to provide a system and device which is susceptible to modular construction so that such units can be transported or even trailer mounted for transportation, for example, to a waste clean-up site.
It would further be advantageous to provide a system and method which can be automated and programmed to process waste streams in a safe manner.
It also would be advantageous to provide a system and method where the waste heat from the pyrolysis and thermal conversion could be used to generate steam and/or power or for other commercial uses.
In this regard there is a need for a system and method which can significantly reduce the volume which need to go to landfill and which can deactivate and stabilize most, if not all, of the toxic components of numerous waste streams.
There is also a need for a system and method that uses indirect heat to reduce wastes, not by burning or incinerating, but in the absence of oxygen.
There is also a need for a system and method that can accomplish these goals, without releasing toxic gases into the environment while additionally producing steam and electricity.